The recent progressive development of high-speed semiconductor devices and progressive increase in the degree of integration require packaging of a plurality of IC chips and circuit parts in a single package. Such a package needs floating, conductive patterns, which are not connected to external terminals, for interconnecting the IC chips and the circuit parts packaged thereon.
A ceramic package body for mounting semiconductor devices is fabricated through steps of forming a plurality of green sheets, forming through holes in the green sheets, printing conductive patterns on the green sheets, laminating and firing the green sheets, and surface-treating the exposed conductive patterns to protect the conductive patterns from oxidation and such. Normally, the exposed surfaces of the conductive patterns are Ni- and Au-plated. In view of facility and efficiency, the exposed surfaces of the conductive patterns are plated by an electrolytic plating process, in which the external terminals are connected to the plating electrodes. However, the conductors of the floating, conductive patterns cannot be plated by the electrolytic plating because they are not connected to the external terminals. Therefore, the conductors of the floating, conductive patterns are plated by an electroless plating process.
The electroless plating process, however, compares unfavorably with the electrolytic plating process in respect of mass-productivity, quality and plating cost. A plating process proposed previously in Japanese Patent Publication (Kokoku) No. 1-38396 to solve the foregoing problems includes the steps of temporarily short-circuiting the terminals of floating, conductive patterns with a conductive paste, supplying current through the conductive paste and the terminals to the floating, conductive patterns in an electrolytic plating bath for electrolytic plating, and removing the conductive paste to disconnect the short-circuited terminals of the floating, conductive patterns.
This known plating process has the following problems.
(1) The conductive paste short-circuiting the terminals must be removed after the completion of the electrolytic plating process and, in some cases, the conductive paste cannot be perfectly removed, which limits the mass-productivity of the plating process.
(2) If the conductive plate is not removed perfectly, the package is rejected.
(3) The conductive paste disperses in the plating bath to contaminate the latter.